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1.
The molecular structure of Cis- and trans-bicyclo[4.2.0]octane in the gas phase was studied. Molecular mechanics calculations applying Boyd's force Held were used for constraining differences between structural parameters during least squares analysis and for calculating vibrational amplitudes. The cyclohexane ring was found to have a distorted chair conformation, the ring in the cis isomer being flattened along the junction and more twisted in the other part. For the trans compound the reverse is true. The following structural parameters were obtained (ra-structure):cis: r(C-C)av. = 1.535 Å. Cyclohexane ring: average bond angle 112.9°; average torsional angle 48°. Cyclobutane ring: average bond angle 88.9°; puckering 157°. The dihedral angle between the bisecting planes of the C(2)-C(1)-C(6)-C(5) and C(8)-C(1)-C(6)-C(7) torsional angles, is 119° - the “connection angle” of the two rings.trans: r(C-C)av.= 1.532 Å. Cyclohexane ring: average bond angle 110.4° ; average torsional angle 57°. Cyclobutane ring: average bond angle 87.3°; puckering 145°. The “connection angle” is 180° (C2 symmetry).Comparison is made with structures of related compounds. 相似文献
2.
The molecular structures of cis-3-hexene and of trans-3-hexene in the gas phase have been determined by electron diffraction combined with molecular mechanical calculations. For cis-3-hexene the data indicate the presence of the (+ac, +ac) and the (?ac, +ac) forms. In trans-3 -hexene three rotamers were observed, with an energy sequence E(+ac, +ac) ≈ E(?ac, +ac) < E(ac, sp). The refined rα0-structural parameters are: cis-3-hexene: C-H = 1.073 Å, CC = 1.330 Å, C(sp2)-C(sp3) = 1.505 Å, ∠CCH(in CH2) = 111.1°, ∠CCC = 111.4°, ∠(CC-C) = 129.1° trans-3-hexene: C-H = 1.078 Å, CC = 1.342 Å, C(sp2)-C(sp3) = 1.506 Å, ∠CCH(in CH2) = 109.3°, ∠CCC = 112.8, ∠CC—C = 124.1°The agreement between calculated and experimental geometries and vibrational amplitudes is good. 相似文献
3.
Quang Shen 《Journal of Molecular Structure》1981,75(2):303-310
The molecular structure and conformation of cis-1,3-dichloro-1-propene have been determined by gas phase electron diffraction at a nozzle temperature of 90°C. The molecule exists in a form in which the chlorine atom of the methyl group and the carbon-carbon double bond are gauche to one another. The results for the distance (rg) and angle (∠α) parameters are: r(C-H) = 1.078(10)Å, r(CC) = 1.340(5)Å, r(C-C) = 1.508(7)Å, r( =C-Cl) = 1.762(3)Å, r(C-Cl) = 1.806(3)Å, ∠Cl-C-C = 111.7°(1.8), ∠(CC-C) = 125.5°(1.5), ∠Cl-CC = 124.6°(1.6) and ∠H-C-Cl = 111°(5). The torsion-sensitive distances close to the gauche form can be approximated using a dynamic model with a quartic double minimum potential function of the form V(Φ) = V0[1 + (4 - 2()2], where Vo = 1.1(8) kcal mol?1 and Φ0 = 56°(5) (Φ = 0 corresponds to the anti form). 相似文献
4.
The structure of 1,1,1-trimethoxyethane has been studied by electron diffraction in the gas phase. Although this technique cannot discriminate between a GGG (point symmetry C3) and a TGG (C1) conformation, vibrational spectra indicate that in the gas phase the C1 conformer is predominant. Constraints necessary for a satisfactory leastsquares refinement were obtained from molecular mechanics calculations. The molecular geometry as obtained from rα-refinements is as follows (rg distances, rα angles; standard deviations in parentheses): r(C-O central = 1.398 (6) Å, r(C-O)terminal = 1.431(6)Å, r(C-C) = 1.527 (6) Å, r(C-H) = 1.114 (1) Å, ∠(C-O-C) = 114.0 (4)°, ∠(O-C-H) = 110.7 (4)°; the C-C-O and O-C-0 angles around the central carbon range between 106.6° and 113.1°. 相似文献
5.
The structure of trimethoxymethane in the gas phase was studied by electron diffraction, ab initio molecular orbital calculations and molecular mechanics. The molecule was found to exist almost exclusively as an asymmetric all-staggered TGG conformer. The electron diffraction structural parameters (rg distances, rα angles) as obtained from geometrically consistent rα-refinements are: r(C-O) central 1.382(6) Å, r(C-O) terminal 1.418(6) Å, r(C-H) 1.112(1) Å, ∠(O-C-O) in the gauche—gauche chain 115.0(1.0)°, in the gauche-anti chains 109.2(0.6)° ∠(C-O-C) 114.3(0.6)°, ∠(O-C-H)Me 109.9(0.3)°, methyl torsion 68(6)°. The structure is adequately reproduced by molecular mechanics calculations applying Allinger's force field. The structures of methoxymethanes can be explained in terms of the anomeric effect. This is confirmed by ab initio calculations. 相似文献
6.
The structure of silyi formate, HCOOSiH3, in the gas phase is determined by electron diffraction. The principal bond lengths and angles (ra) are r(Si-O) = 169.5 ± 0.3 pm, r(C-O) = 135.1 ± 0.6 pm, r(C O) = 120.9 ± 0.7 pm, ∠(C-O-Si) = 116.8 ± 0.5°, ∠(OC-O) = 123.5 ± 0.5°. The silyi group is twisted by 21° away from the planar cis conformation but there is nevertheless a very short (286.5 ±1.0 pm) non-bonded Si ·O contact. 相似文献
7.
The molecular structure and conformation of diisopropylamine have been determined by gas electron diffraction with the aid of vibrational spectroscopy and molecular mechanics calculations.Only one conformer with the skeletal geometry of C2 symmetry has been detected. The dihedral angle, CNCH, has been determined to be 52(4)°. The difference between the NCC angles at the gauche and trans positions with respect to the opposite NC bond is 2.4°. The CNC bond angle, 120.1(10)°, and the CN bond length, 1.470(4) Å, are 8.3° and 0.014 Å larger than the corresponding values of dimethylamine respectively 相似文献
8.
9.
L.H. Boonstra F.C. Mijlhoff G. Renes A. Spelbos I. Hargittai 《Journal of Molecular Structure》1975,28(1):129-135
The molecular structure of tetramethoxysilane was determined in the gas phase by electron diffraction. The molecule has S4 symmetry, slightly flattened along the axis. The SiO bonds are shorter than in methylsilylether, demonstrating the effect of electronegative substituents on the Si atom. The geometrical parameters (ra structure) are: Si-O bond 1.613 Å; C-O bond 1.414 Å; C-H bond 1.12 Å; O-Si-O angle bisected by S4 axis 115.5°; Si-O-C angle 122.3°; O-C-H angle 111°; methoxyl torsional angle 64°; methyl torsional angle 60°. 相似文献
10.
11.
Quang Shen 《Journal of Molecular Structure》1983,102(3-4):325-332
Dichlorotetramethyldisiloxane is studied by gas-phase electron diffraction at room temperature. The least-squares values of the bond distances (rg) and bond angles () are: r(C---H)=1.084(5) Å, r(Si---O) = 1.624(2) Å, r(Si---C) = 1.852(2) Å, r(Si---Cl) = 2.067(2) Å, SiOSi = 154.0° (1.5), ClSiO = 110.2° (0.8), ClSiC = 109.6°(0.7), HCSi = 111.7°(1.5), OSiC = 110.0°(0.8), τ1 (zero corresponds to the Si---Cl bond trans to the Si---O---Si linkage) = 78°(6) and τ2 = 141°(19). A two-conformer model cannot be ruled out. 相似文献
12.
Ala’Eddin Alsarabi 《Tetrahedron letters》2004,45(49):9003-9006
A new and highly stereoselective access to 4,10b-trans or 4,10b-cis hexahydropyrido[2,1-a]isoindole derivatives is reported, both requiring an intramolecular Mannich-type reaction as key step. The cis diastereoisomer is obtained in three steps from a 2-alkyl benzaldehyde through the stereoselective formation of a 2,6-cis-disubstituted piperidine, while the trans stereomer is efficiently obtained, in a single step, if a 2-formyl benzoic acid is involved in the Mannich cyclization process. 相似文献
13.
The electron diffraction data of cycloheptanone, collected at 371 K, can be explained using a model of partial pseudorotation, with the symmetrical twist—chair as the mean structure. Therg, rα-structure is characterized by r(C-C) = 1.536 Å, r(C=O) = 1.219 Å, r(C-H) = 1.124 Å, xxxCC(sp2)C = 117.3°, xxx(CCC = 115.5° and xxx(HCH = 103.2°. Approximate values for the constants of the pseudorotation potential are included. 相似文献
14.
Efficient routes for the gram-scale preparation of the proline analogues that bear a phenyl substituent attached to the pyrrolidine β carbon (cis- and trans-β-phenylproline) have been developed. The cis derivative was synthesized from N-Boc-β-alanine in six steps and 78% overall yield. The generation of a vinyl triflate with full regiochemical control together with a high-yielding cross-coupling reaction and a completely stereoselective hydrogenation are at the basis of the high efficiency of the procedure. Epimerization of the cis β-phenylproline derivative with lithium bis(trimethylsilyl)amide provided access to the trans isomer. 相似文献
15.
Irradiation of acetone solutions of trans-chlordane (4a) and trans-nonachlor (4b) with UV light produces new half-cage photoisomers (5a or 6a and 5b or 6b, respectively) with bridging that differs from that of the photoisomers (2 and 8a) obtained from cis-chlordane (1b) and heptachlor epoxide (7). A new photoisomer (10) obtained from heptachlor epoxide is transformed into photoisomer 8a on further irradiation. Detailed PMR and 13C-NMR studies establish the structures of the new photoisomers and permit a decision between alternative formulations for the structures of the half-cage photoisomers of heptachlor epoxide and cis-chlordane, 相似文献
16.
The molecular geometry of selenium oxychloride has been studied by electron diffraction. The internuclear distances (in terms of ra) are: r(Se-O) 1.612 ± 0.005 Å, r(Se-Cl) 2.204 ± 0.005 Å, r(Cl β O) 3.064 ± 0.012 Å, r(Cl β Cl) 3.295 ± 0.016 Å. The bond angles are ∠Cl-Se-O 105.8 ± 0.7° and ∠ Cl-Se-Cl 96.8 ± 0.7°. The structural parameters of three simple selenium-oxygen compounds are compared with those of their sulphur analogs in terms of the valence shell electron pair repulsion model. 相似文献
17.
Quang Shen 《Journal of Molecular Structure》1985,130(3-4):275-282
The molecular structure of gaseous epichlorohydrin has been investigated using electron diffraction data obtained at 67°C. The conformational composition at this temperature is such that the molecules exist predominantly in a gauche-2 conformer (where the C---Cl bond is 160° away from the C---O) bond). Refinements showed that 33% (σ = 4) of the molecule exist in the gauche-1 form. The important distances (rg) and angle () with the associated uncertainties are r(C---H) = 1.095(5) Å, r(C---O) = 1.442(3) Å, r(C---C) = 1.475(8) Å, r(C---CM) = 1.523(7) Å, r(C---Cl) = 1.788(2) Å, CCO = 114° (1), CCCM = 119°(1), ClCC = 108.9° (7), and Tau(ClCCO) = −150°(10) (gauche-2) and Tau(ClCCO) = 78° (10) (gauche-1). 相似文献
18.
The molecular structure of N(C2H5)2(SiH3) in the gas phase has been determined by electron diffraction. The SiNC2 skeleton is a shallow pyramid, with angles CNC 114.5(12)° and SiNC 120.9(5)°, and the methyl groups lie so that one CC bond lies close to the CNC plane, but the other is almost perpendicular to it. Other important parameters (ra) are: r(SiN) 171.5(3), r(CN) 145.6(4), r(CC) 154.3(8) pm, and ∠NCC 113.6(6)°. 相似文献
19.
The electron diffraction study of tetramethoxymethane showed that in the gas phase the molecule has S4 symmetry, flattened along the S4 axis. Central and peripheral C-O bond lengths are different, consistent with considerations based on the anomeric effect. Comparison is made with ab initio calculations on methanediol. The geometrical parameters (rg(1) structure) are: central C-O bond 1.395 Å; peripheral C-O bond 1.422 Å; C-H bond 1.11 Å; O-C-O angle bisected by the S4. axis 114.7°; C-O-C angle 114.0°; O-C-H angle 111.9°; methoxy torsional angle 63.1°; methyl torsional angle 48.5°. 相似文献
20.
Neil K. Garg 《Tetrahedron letters》2005,46(14):2423-2426
A facile formal total synthesis of dragmacidin B, trans-dragmacidin C, and cis- and trans-dihydrohamacanthins A is presented. Our approach to these bis(indole) alkaloids involves a one-pot, four-step cross-coupling/deprotection sequence where complete halogen selectivity is observed. A related approach to access the dihydrohamacanthins is also described. 相似文献